Sheet materials, in particular sheet vinyl flooring products, made with chips or particulate material, are commonly referred to as inlaids. These products and processes for their manufacture are well known in the floorcovering business and originate back to the early linoleum times where through patterned floorcoverings, based on linseed oil, cork dust and resins were developed by the industry. The process was later modified for vinyl.
Vinyl inlaid floorcovering consists of coarse colored particles, such as chips or dry blends, which are "laid on" a substrate and then sintered by heat, or "laid in" a transparent liquid or solid matrix and fused by heat. The chips are produced from pre-gelled or fused spread, calendered or extruded compounds cut into geometrically regular profiles or ground into randomly shaped particles.
The dry blends are made by mixing fine PVC powder with plasticizer, filler and color pigments and heating above the PVC compound's softening temperature. The small original particles "grow" and form a loose, porous, coarse, fluffy mass.
Currently, to produce realistic inlaid patterns for sheet vinyl, conventional manufacturing procedures distribute the coarse particles on the substrate in different steps with the help of area-complementary stencils, followed by topcoating with a clear wearlayer. This method is complicated and can only be used to produce large geometric patterns.
The inlaid floorcoverings are normally characterized as those which maintain their decorative appearance as the surface is worn or abraded away. This characteristic makes such products particularly suitable for use in commercial areas where significant wear is encountered.
Modern inlaids generally fall into two classifications: resilients and non-resilients. Resilients include a substantially continuous layer of foam and are usually made by incorporating solid particulate material into a plastisol coating, followed by gelling and fusing. Non-resilients do not contain a foam layer and usually are made by sintering and/or calendering, or otherwise compacting, particulate material.
The non-resilient products commercially offered are those containing large (about 1/8 inch) square chips in a clear matrix and those containing small (about 0.004 inch) dry blend resin particles made by sintering and/or compacting normal dry blend resins. It is believed that the reason no products containing chips, granules, or particles of an intermediate particle size (e.g. ranging from about 0.004 inch to about 0.04 inch) are offered results from limitations inherent in current inlaid manufacturing technology, discussed more fully hereinafter.
While construction of inlaid products by compaction from discreet chips or particles (normally of different colors) offers distinct styling opportunities, a significant premium is paid in terms of expensive, cumbersome equipment. Furthermore, the nature of the process restricts the range of designs available. For example, in order to effect specific registered pattern definition, it is necessary to deposit chips of different colors in preselected areas on the sheet. This is difficult mechanically, and results in a slow cumbersome process which does not produce finely defined designs.
Some of the inherent difficulties in current production techniques for non-resilient inlaids have been minimized by use of increasingly sophisticated materials and design techniques, such as using fine particle size, dry blend resins, printing over the surface of the resulting inlaid product, optionally, embossing, with and without application of a wearlayer. Unfortunately, whereas the use of the finer particle size preserves the specific characteristic of an inlaid product, i.e. the pattern does not change as the product wears through, overprinting the product, whether or not a wear layer is applied, essentially negates this characteristic because wearing through the print layer essentially destroys the pattern. This eliminates the product from commercial, high-use environments and limits its utility principally to styling effect in residential and related applications.
Resilient inlaids are usually made by embedding ground plastic particulate material in a plastisol coating. U.S. Pat. No. 4,212,691 exemplifies such products and methods for their manufacture. As taught in this patent, the thickness of the particles of the decorative chips or flakes is stated to be from about 3 mils to about 25 mils (e.g. see column 7, lines 62-64). However, it is the length of the particle, i.e. its largest dimension, rather than thickness that is observed when viewing the pattern. That dimension is stated to be from about 50 to 500 mils at column 8, lines 17-18. It is to be noted that the products disclosed all contain embedded chips or flakes ground from plastic sheet stock, even when chips or flakes from other stock materials are added (e.g. see column 8, lines 4 et seq). These chips or flakes characteristically have a high aspect ratio (i.e. length/thickness).
Thus, existing inlaid technology, although capable of producing commercially satisfactory inlaid products, has limitations and deficiencies. State of the art inlaid technology for "chip" products first grinds the chips from plastic sheets. This predefines the particle shape and is expensive. Furthermore, spherical particle shapes can not be made by the grinding techniques currently in use for inlaids.
Additionally, products formed by compacting or sintering dry blends have always shown limited particle distinction due to process limitations and available particle sizes. The particles tend to lose their identity due to agglomeration or lumping caused by the sintering process.